1. Field of the Invention
The present invention relates to methods and systems for filtering generally-broadcast messages based on the applicability of the message to the receiver of the message. More particularly, the present invention relates to methods and systems for filtering generally-broadcast messages based on current spatial position, previous path trajectories, and probable destination.
2. Background Art
In general, region-specific information is disseminated by pre-determined point-to-point communication or by a general broadcast that must be manually monitored in order to extract information relevant to a specific position, velocity and time of interest. For example, marine weather data is continuously broadcast and mariners must monitor the broadcast for long periods of time in order to obtain the information specific to their region. Even then, the exact region affected may require computation or may be ambiguously defined. There is also the possibility that a user may miss information of interest because he or she occupies an unknown location, is unfamiliar with the region, or uses a different frame of reference.
Another example of region-specific information is a tactical ballistic missile (TBM) warning, which is derived from space-based and ground-based sensor data and which is provided through a variety of broadcast and general purpose communications systems to a small subset of in-theater combat forces. Currently, such warnings require transportable processing stations that can generate information about specific situations in the field but cannot directly communicate with all affected individuals. The timeliness, reliability, and dispersion of information under these conditions are of concern, especially since the warnings are in the form of geographical coordinates and time of predicted impact, and users must interpret the data to determine if the warning affects them.
An additional example of region-specific information is generally-broadcast information received by motorists, including information concerning road conditions and advertisements from merchants within a specific geographical region. Motorists must generally determine their current position and review the broadcast information for long periods of time to obtain information that is relevant to the current position. While tedious to a motorist traveling on a familiar route, the need to simultaneously determine current position and determine the relevance of the received messages can be especially daunting to motorists along unfamiliar routes. Further, the motorist must review the received messages for relevance not only to current position, but also with respect to a probable destination.
A number of commercial systems use external positioning systems, such as a global positioning system (GPS) or a LORAN system, to select relevant data from computer-based files. Examples of such computer-based files include electronically-stored maps for use in automobiles. These commercial systems are useful for relatively static information but fail to address dynamic factors, such as environmental events, combat factors, and other location-specific information.
Further, a number of existing systems use spatial position data obtained from external positioning systems to selectively filter region-specific information received by a remote unit. For example, U.S. Pat. No. 5,243,652 to Teare, et al. discloses a database access system in which each mobile user has a positioning system that transmits position information to a central facility. This central facility then grants or denies database access depending on the geographical location of the mobile user. U.S. Pat. No. 4,860,352 to Laurance, et al. discloses a system in which a satellite system determines the position of a transmitter at a first location and a receiver at a second location. The transmitter position is appended to the received message which is sent by the satellite system to the receiver. The receiver receives the appended message, extracts the transmitter position data and compares the extracted transmitter position with a stored transmitter position. If the positions correlate, the receiver knows it has received an authentic message.
U.S. Pat. No. 5,636,245 to Ernst, et al. and U.S. Pat. No. 6,522,250 to Ernst, et al. concern improvements over these existing systems and disclose filtering systems that determine the relevance of generally-broadcast information based on the location, velocity, and time of an object or event of interest. The disclosed systems include a general broadcasting unit comprising a transmitter for broadcasting messages that includes an information segment comprising a region, velocity and a time corresponding to an event. A remote unit includes a receiver for receiving the broadcast messages and storage means for storing spatial position information relating to the remote unit. The stored data selection information is related to information contained in the broadcast segment and is compared with the latter in the matching processor and used, along with spatial position information, to determine whether a match condition is satisfied. If so, the message is disseminated to a user.
A number of existing systems selectively filter generally-broadcast messages received by a movable unit based on probable future positions of the movable unit. For example, U.S. Pat. No. 5,293,163 to Kakihara, et al. discloses a navigation apparatus for use in vehicles that displays road information, such as current traffic information and parking conditions, to a user through an on-board display device. The navigation system is designed to selectively display the road information that is relevant to both the current position of the vehicle and a probable destination of the vehicle. The probable destinations of the vehicle are derived from locations within a fan-shaped area that fans out from the current spatial position of the vehicle in the direction of travel through a pre-determined angle. As such, the fan-shaped area identified a number of potential destinations for the vehicle based only on current position and travel direction.